Generally, as shown in FIG. 16, a magnetic disk drive is provided with a magnetic head assembly 3, which further comprises a magnetic head slider 1 and a suspension, a magnetic disk 2, magnetic disk rotation drive means 16, such as a spindle motor, and an actuator mechanism 13 (including a bearing 14 and voice coil motor) for moving the magnetic head assembly 3 along the information recording surface of the magnetic disk 2, which are housed in a body 17 made of such metal as an aluminum alloy.
FIG. 17 is a diagram viewing the magnetic head assembly 3 from the magnetic disk side, and FIG. 18 is an exploded perspective view of the magnetic head assembly 3 in FIG. 17. In FIG. 17 and FIG. 18 the suspension 4 comprises a flexure 5 further comprising a plate spring 9, which is a plate holding the magnetic head slider 1 at the tip area and a flexible circuit 8, and a load beam 10 for supporting the tip of the flexure 5 with a dimple 12.
The magnetic head slider 1 has a magnetic read/write element for reading and writing data from/to the magnetic recording medium, and which very slightly floats over the magnetic disk 2 by an air flow which is generated by the rotation of the magnetic disk 2. The magnetic head slider 1 comprises a positive pressure generation section and a negative pressure generation section on the surface facing the magnetic disk 2, which are designed such that the floating profile on the entire magnetic disk 2 becomes constant under a predetermined temperature and pressure, because of the static load from the suspension 4 and the balance of the positive pressure and negative pressure generated by the magnetic head slider 1.
Conventionally the operating temperature range of a magnetic disk drive is limited to 5° C. to 55° C., for example, in terms of the reliability of the device and magnetic reading/writing, and normal operation is guaranteed on the assumption that the user of the magnetic disk drive will pay attention to the operation environment thereof.
In the case of a magnetic disk drive installed in a car navigation system, for example, the magnetic device is installed directly behind a motor fan, for example, in the car navigation system, so that when temperature is higher than the guaranteed temperature range of the magnetic disk drive, air cooling is performed by the motor fan, and when the temperature in the car navigation system abnormally rises, the magnetic disk drive and car navigation system shut down so as to avoid the loss of information on the magnetic disk drive. On the other hand, if the temperature is lower than the guaranteed range, the coercivity of the magnetic disk 2 increases, which makes writing difficult even if the reading of information is without problems, so the writing operation is disabled until the temperature of the magnetic disk drive becomes higher than the predetermined temperature by the heater of the vehicle main body (e.g. see Masahiko Takizawa and other: “Application of HDD to navigation”, Pioneer Technical Information Magazine, 2002, Vol. 12, No. 1 [Online] [searched on Oct. 1, 2002], Internet <http://www.pioneer.co.jp/crd1/rd/pdf/12-1-3.pdf>).
A reason why the operating temperature range of the magnetic disk drive is limited to about 5° C.–55° C. is that the coercivity of the magnetic disk 2, which records and holds information, has a temperature dependency, as described above (e.g. see Tao Pan, Geoffrey W. D. Spratt, Li Tang, Li-Lien Lee, Yong Change Feng and David E. Laughlin, “Temperature dependence of coercivity in Co-based longitudinal thin-film recording media,” J. Appl. Phys., 81 (8), 15 Apr. 1997, pp. 3952–3954, [online], [searched on Oct. 1, 2002], Internet <http://neon.mems.cmu.edu/laughlin/pdf/201.pdf>), and since the current recording density of the magnetic disk drive reaches 50 gigabit/inch square, it is said that the increase of the recording density is about 100% at an annual rate, and as the recording density increases the magnetic disk drive has been optimized by increasing the coercivity of the magnetic disk 2 in order to hold the recording information stably in this small recording area. FIG. 19 shows an example of the temperature dependency of the coercivity of the magnetic disk 2. In the example of FIG. 19, the coercivity increases about 9% by decreasing the temperature from room temperature (25° C.) to −25° C., and the coercivity decreases about 10% by increasing the temperature from room temperature (25° C.) to +75° C. The coercivity changes about 19% in the temperature range of −25° C. to +75° C., and the coercivity changes about 29% in the temperature range of −50° C. to +100° C. Therefore when data is recorded in a low temperature status using a magnetic head slider 1, which was optimized to appropriate overwrite characteristics in a room temperature status, sufficient writing cannot be performed in a coercivity from the head slider 1, and when data is recorded in a high temperature status, on the other hand, the leakage magnetic field from the magnetic head slider 1 becomes relatively too high with respect to the coercivity of the magnetic disk 2, and the area to be recorded by the magnetic head slider 1 becomes larger than the area to be recorded at room temperature, so such a problem as overwriting the recording information on an adjacent area occurs. Therefore in the present status the operating range of the magnetic disk drive is limited to about 5° C.–55° C.
The change of temperature in the magnetic disk drive also influences the flying height characteristics of the magnetic head slider 1. FIG. 20 shows a typical shape of the magnetic head slider 1. The magnetic head slider 1 comprises an inflow end 18 of air at the front part and an outflow end 19 of air at the back part, and an air bearing surface is created using the air flow which flows into the micro-space between the magnetic head slider land the magnetic disk 2. Specifically, the magnetic head slider 1 has steps 21 at the inflow end 18 and at the front part of the surface facing the magnetic disk 2 of the magnetic head slider 1 which protrudes the most, these steps are called the rail 22 and the pad 23, and positive pressure is generated at the area called the rail 22 and the pad 23 by compressing air which flows in from the inflow end 18, and negative pressure is generated at a concave area called the cavity 24. Also a magnetic reading/writing element 20 is installed near the outflow end 19.
The magnetic head slider 1 has a curved surface called the crown, and this crown shape deforms according to the temperature, which depends on the difference of thermal expansion coefficients between the material of the magnetic head slider 1 and that of the plate spring 9, which is a thin plate used to adhere to and support the magnetic head slider 1. Normally this crown shape deforms in the plus direction indicated by the arrow mark in FIG. 20(b) at low temperatures, in other words the convex section protrudes more, and the crown shape deforms in the minus direction at high temperatures, in other words the convex section flattens (e.g. see Japanese Patent Application Laid-Open No. H9-231698, page 9, FIG. 11 and FIG. 12).
The influence of the change of the crown on flying height can be determined by actually measuring the flying height or by numerical analysis, but it is known that the flying height increases as the crown changes to the plus, and the flying height decreases as the crown changes to the minus.
At the moment the amount of air gap between the magnetic head slider 1 and the magnetic disk 2, that is the flying height of the magnetic head slider 1 with respect to the magnetic disk 2, drops to about 15 nm to implement high recording density, and one factor causing contact between the magnetic head slider 1 and the magnetic disk 2 is the change of flying height, which is caused by the change of the crown due to the change of temperature. As a technology to decrease the change of flying height caused by temperature, a technology of using a temperature compensation element to stabilize the change of the crown value caused by temperature was disclosed (e.g. see Japanese Patent Application Laid-Open No. H7-153049). Also a technology of using the difference of the thermal expansion coefficients between the plate spring 9, which is a thin plate for adhering the magnetic head slider 1, and the magnetic head slider 1, so as to stabilize the change of the crown value by temperature, was disclosed (e.g. see Japanese Patent Application Laid-Open No. H7-320435, Japanese patent Application Laid-Open No. H7-65525 and Japanese Patent Application Laid-Open No. H7-307068). By using these technologies, the change of the crown value of the magnetic head slider 1 caused by the change of temperature can be suppressed.
As a prior art to solve the problem of the reliability of magnetic reading/writing which is caused by the change of the coercivity of the magnetic disk 2 due to the change of temperature, and the problem of the reliability of the magnetic disk drive caused by the flying height of the magnetic head slider 1 due to the change of temperature, a technology of providing a temperature sensor and heater and a Peltier element to the magnetic disk drive so as to heat and cool according to the external temperature, and providing a double structured outer shell so that the internal environment is independent from the external environment, was disclosed (e.g. see Japanese Patent Application Laid-Open No. 2002-245749). By using this prior art, the internal environment can be controlled independently from the external environment, and the magnetic disk drive can be used under wider external environments without diminishing the reliability.
Thus far magnetic disk drives have been largely used indoors, and the operation guaranteed temperature range of 5° C. to 55° C. caused little problems for magnetic disk drives. However now applications which are different from conventional usage are already emerging, such as installing a magnetic disk drive in a car navigation system, and it is expected that using magnetic disk drives under more severe environments will increase. For example, under extremely low temperatures below −20° C., or at high temperatures exceeding 70° C., conventional magnetic disk drives have problems of reliability of magnetic recording because of the temperature dependency of the coercivity of the magnetic disk 2, and there is the problem of reliability of the magnetic disk drive in terms of the stability of the flying height of the magnetic head slider.
Another technology disclosed is making the magnetic disk drive independent from the change of the environment outside the device, and controlling the magnetic disk drive using a temperature sensor and a heating/cooling mechanism, so as to support a wide range of external environments, but with this configuration not only these additional elements are required but also a delay is generated when the magnetic disk is started because temperature is controlled for the internal temperature of the magnetic disk drive to be within an operable range. If a double structured outer shell is used to make the external environment and internal environment independent from each other, the size and weight of the magnetic disk drive itself increases, which is not appropriate for an application where portability is important.
For stabilizing flying height, a technology for controlling the change of flying height of the magnetic head slider 1 caused by the change of the temperature by decreasing the change of the crown value caused by temperature was disclosed, but in the case of the current magnetic head slider 1 using negative pressure, if the change of the crown value is decreased with respect to temperature, then the stability of flying height cannot be uniform on the entire surface of the magnetic disk 2, and this was clarified by an analysis of the flying height of the magnetic head slider 1 using a modified Reynolds equation by the present inventor. FIG. 21 shows the analysis result of the flying height of the magnetic head slider 1 with respect to the change of temperature when the crown value does not change. The abscissa indicates the position of the magnetic head slider 1 in the radius direction with respect to the magnetic disk 2, and the ordinate indicates a normalized flying height which was normalized by the flying height of the magnetic head slider 1 at 25° C. At high temperatures the flying height becomes high when the magnetic head slider 1 is at the outer periphery of the magnetic disk 2, and at low temperatures the flying height becomes high when the magnetic head slider 1 is at the inner periphery of the magnetic disk 2. The change of flying height caused by temperature is highest at the outer periphery, which is 10%, and the flying height changes about 8% from the inner periphery to the outer periphery at the time of low temperatures and at the time of high temperatures. This large change of flying height from the inner periphery to the outer periphery is not desirable in terms of both the reliability and efficiency of magnetic reading/writing and the reliability of the magnetic disk drive. In other words, if the flying height changes considerably from the inner periphery to the outer periphery, the spacing loss factor of the magnetic reading/writing caused by flying cannot be uniform between the inner periphery and outer periphery, and the efficiency of the magnetic reading/writing deteriorates at a position of the inner periphery or outer periphery where the flying height increases. In terms of the reliability of magnetic reading/writing, if the flying height drops further at the inner periphery side when the coercivity of the magnetic disk 2 is dropping at high temperature status, for example, the write magnetic field could become too strong. In terms of the reliability of the magnetic disk drive, the flying height decreases at the outer periphery at low temperatures, and the flying height decreases at the inner periphery at high temperatures, so the contact of the magnetic head slider 1 and the magnetic disk 2 is a concern at both low temperatures and high temperatures, and optimization for the reliability of the magnetic disk drive is required for both low temperatures and high temperatures, which makes optimization of the magnetic disk drive difficult.
With the foregoing in view, it is an object of the present invention to provide a magnetic disk drive which decreases the difference of the change of the flying height at the inner and outer peripheries of a magnetic head slider 1 caused by the change of temperature, and can operate in environmental conditions which are wider than prior art without using an outer shell and the additional elements of a heating and cooling mechanism, and without causing a delay due to temperature control at startup of the magnetic disk drive, and a magnetic head assembly 3 to be used for this magnetic disk drive.